This invention relates generally to the non-contact direct printing of thin film features or patterns of electronic materials for the modification, customization and/or repair of display and microelectronic circuits, in particular, non-contact repair of micro-circuits such as required in the repair of flat panel displays.
For many applications, in particular the additive modification of electronic circuits fabricated using semiconductor processing technologies, as in the example of, vacuum deposition of the required materials or patterning using lithographic batch processes, there is a need for a process capable of generating a repair pattern to fix a defect on the existing circuit once it has been completed. For the additive modification to be compatible with the existing circuit, the material deposited must be of similar thickness, width and functionality as the already existing patterns. More specifically, the repair typically must satisfy “thin-film” characteristics; that is, have thickness of less than one micrometer, and more often less than 0.5 micrometer, and have line width of 5 micrometers or less. The only processes currently available for correcting manufactured circuits with additive thin film material in this range of dimensions require the presence of a vacuum. Examples of these vacuum processes include laser chemical vapor deposition (LCVD), focused ion beam (FIB) deposition and vacuum laser induced forward transfer. These techniques are used with limited success due to their complexity, limited choice of materials and slow deposition speed for the repair of patterned circuits on semiconductor wafers and lithography chrome masks. For large area circuits such as flat panel displays, only LCVD has been adapted for repair applications.
Atmospheric pressure and room temperature additive material methods or processes are typically limited to direct printing of electronic materials, for example, metal conductors, polymer, or ceramic dielectrics. Such processes require the use of functional rheological systems, as described in U.S. Pat. No. 6,805,918 (the '918 patent) and U.S. Pat. No. 7,014,885 (the '885 patent). More specifically, rheological systems are defined as the class of material with properties that lie in a range between solid and liquid, and are characterized by at least one fundamental rheological property such as elasticity or viscosity. Further, the rheological materials include but are not limited to gels, pastes, inks, concentrated solutions, suspensions, Newtonian and non-Newtonian fluids, viscoelastic solids and elastoviscous fluids. The rheological materials may include but not be limited to metal or non-metal including insulators as well as biological materials. The rheological materials are homogeneous mixtures and typically include (for example) functional materials, solvent or vehicle, chemical and rheology precursors, binders, surfactants, dispersant agents, powders, and/or biomaterials. The functional material is the material that contains the functional properties (such as electrical, magnetic, and so forth) of the desired deposit. The rheological materials may be metal or non-metal materials with particle sizes ranging from 5 to 500 nanometers and suspended within one or more solvents and/or binders, and having viscosity in the range of approximately 1 cP to 1,000,000 cP.
Depending on the dispensing technique selected, the viscosity of the rheological system has to be chosen carefully. The viscosity can range from water-like inks with viscosities of 1 to 100 cP to thicker inks with medium to high viscosities (greater than 100 to approximately 100,000 cP) to thick pastes having viscosities greater than 100,000 cP. Inkjet inks have viscosities of approximately 5 to 20 cP at the jetting temperature. Screen printing inks may have viscosities of approximately 2000 cP, while screen printing pastes may have viscosities greater than about 50,000 cP.
Dispensing methods and techniques utilizing low viscosity inks include inkjet printhead droplet-on-demand dispensing technologies using piezoelectric, thermal, electrostatic, acoustic, or other drives. These methods have been well documented and use inks having viscosities less than 1000 cP, and usually less than 50 cP. Production-level inkjet applications typically dispense droplets in the tens of picoliter volume or more. Ten picoliters is equivalent to approximately a 26 micrometer diameter sphere. A thin film feature that is 5 micrometers in diameter by 0.3 micrometers thick has a volume of approximately 6 femtoliters, and the equivalent drop (sphere) is approximately 2 micrometers in diameter. Apparatus to create this droplet size is not yet available outside of research laboratories, and this small volume can be produced only with certain fluids not necessarily compatible with electronic materials or applications. Though developments continue, inkjet technologies for very fine line widths have not yet been proven for production.
Current shortcomings of inkjet droplet-on-demand methods to achieve lines less than 10 micrometers in width include: (i) apparatus compatibility limited to materials having viscosities less than about 1000 cP and more typically less than 50 cP, which further implies (ii) low metals content and thus (iii) further requires multiple passes to achieve conductivity requirements, impacting throughput; (iv) apparatus capability limited to producing a mean of droplet distribution of greater than or equal to approximately 5 micrometer diameter, which limits minimum line width to approximately 7 micrometer; and (v) multiple factors determining line width size and edge integrity include mean of droplet distribution, ink viscosity, ink/substrate contact angle, substrate surface energy, substrate surface morphology, printing and drying temperature.
Laser transfer or laser direct printing methods of functional rheological systems are described, for example, in US patents '918 and '885, and U.S. Pat. No. 8,025,542 (the '542 application). FIG. 1 shows a conventional apparatus 100 required for laser transfer of rheological materials. The coating to be transferred 108 is applied to a transparent substrate, or ribbon, 106 facing the receiving substrate 104. The ribbon serves as a supporting structure for the coating, and must be optically transparent to the laser wavelengths in use. A pulsed laser beam 116 is directed through focusing optics such as an objective lens, or final lens, 102 at the ribbon surface opposite the coating, and the coating is transferred to the receiving substrate 104. A transferred pattern 110 is formed on the receiving substrate by moving the receiving substrate 104 with respect to the laser 116, and moving the ribbon relative to the laser such that a coated region is always available for transfer. The transferred pattern on the receiving substrate may require curing (not shown). Typically, the ribbon extent is larger than the laser beam that impacts it. As shown in FIG. 1A, the coating on the transparent ribbon is held at a fixed distance from the receiving substrate, and the pulsed laser propels the released coating layer across the gap.
Key parameters for laser direct printing include (a) the nature of the material to be transferred, (b) the laser energy density, and (c) the transfer mechanics which depends on both the nature of material and available energy. For example, the MAPLE-DW process as described in U.S. Pat. No. 6,177,151 (the '151 patent) and U.S. Pat. No. 6,766,764 (the '764 patent) combines a transfer material with a matrix material, which specifically has the property of being more volatile than the transfer material when exposed to pulsed laser energy. The transfer materials may include but not be limited to metals or non-metals including insulators as well as biological materials. The coated material (matrix plus transfer materials) is assumed to be in solid state during the deposition process. Transfer energy densities for metals using the MAPLE-DW process cited in '151 and '764 are typically 300 to 500 mJ/cm2. The MAPLE-DW transfer mechanism consists of volatizing or vaporizing the matrix material, which then causes desorption of the transfer material from the supporting ribbon to the receiving substrate. The MAPLE-DW process assumes that after transfer, the deposited material needs no additional processing.
In the '918 patent examples, transfer energy densities for metals using the rheological material transfer process were cited as 400 to 500 mJ/cm2. The rheological material transfer mechanism as described by the '918 and '885 patents consists of the following steps, and as shown schematically in FIGS. 2A and 2B: (a) the laser energy 116 locally heats a very small volume of the rheological fluid 202 near the supporting ribbon surface, and then (b) the vaporized material generates a high pressure burst that propels the non-vaporized fluid 110 forward to the receiving substrate 104. The material that is transferred is substantially unchanged rheological fluid. Most deposition materials require post-processing steps such as thermal, photothermal, or photolytic processes to decompose any chemical precursors, or drive off solvent vehicles, or consolidate or densify or sinter the functional materials and permanent binders.
Further, the jetting effect described in U.S. Pat. No. 6,815,015 (the '015 patent) occurs under narrow process window conditions using rheological fluids. Specifically, the transfer energy density is tailored to control the transfer process so that the material transferred remains roughly the same size or smaller than the incident laser beam profile. Transfer energy density for the jetting process reported in the '015 patent is less than 100 mJ/cm2. Operation in the jetting window is advantageous in that feature sizes comparable to the incident laser beam size may be created. However, the conditions for jetting behavior as described in the '015 patent requires relatively thick coatings (1 to 20 micrometers thick, and more specifically 5 to 10 micrometers in the cited example) on the transparent ribbon. This relatively large volume of rheological fluid is required to form the neck or jet shown in FIG. 6D of the '015 patent, and shown schematically as 204 in FIGS. 2C and 2D of the present application. The result is equally thick transferred features, far larger than the submicron thickness required for thin film repair. In addition, to form the neck or jet 204, the rheological fluid must exhibit fluid properties with viscosities well below 100,000 cP, and more likely, less than 10,000 cP. Then, due to the droplet-like properties of the transfer generated under the jetting regime, the resulting transfers will exhibit a large amount of debris or splashing 112 outside the intended transfer feature 110 when the jetting droplets strike the surface of the receiving substrate. Thus, a further limitation of operation in the jetting regime of a laser transfer approach is that it cannot produce well defined narrow features or patterns with consistent and repeatable straight edges, as required for thin film repair of microcircuits.
Key parameters required to print features with thin film characteristics, that is, five micrometer line width by sub-micrometer thickness with well defined and straight edges and uniform thickness using rheological materials include, for example, (i) material size, uniformity and thickness on the ribbon substrate (material transfer methods) or delivered droplet size (aerosol jet or ink jet), (ii) material flow at the receiving substrate surface, which can be a function of delivery or substrate temperature, viscosity, substrate material, surface morphology or roughness and surface energy conditions, (iii) relative position of the delivery mechanism to the receiving substrate. In the case of an ink jet system or a laser forward transfer system operating in the jetting regime, for example, too large a distance may result in excessive line width (due to spreading of droplets) while too close a distance may also result in excessive line width due to poor line edge definition (caused by splatter of the droplets). Additional parameters that must be considered in direct printing of thin five micrometer wide lines with good line edge definition using rheological materials include: (iv) material particle size in the ink or rheological material, for metals, typical metal particles sizes should be in tens of nanometers or less, (v) aperture size in delivery mechanisms, and (vi) beam size, (vii) energy density and uniformity, and (viii) wavelength of the laser or energy source.
Conventional direct printing techniques fall short of the requirements to produce narrow features with thin film characteristics as those required for the modification, customization and/or repair of display and microelectronic circuits, in particular, non-contact additive material repair of micro-circuits such as required in the repair of flat panel displays. The jetting regime described in the '015 patent does not meet the thin film requirements and is not suitable for use in forming thin film line features that are nominally five or less micrometers wide and have sub-micrometer thicknesses.